The subject matter of the present invention relates generally to portable bridges that can be transported to the bridge site as two separate longitudinal bridge sections which are joined together at the site. In particular the invention relates to such a portable bridge in which the longitudinal bridge sections are fixedly secured together by pivotable diaphragm members which are bolted in place at both ends after installation of the bridge sections.
The portable bridge of the present invention is especially useful on logging roads and is of heavy duty construction to carry logging trucks and other large heavy equipment vehicles. The bridge is made of different lengths between 30 feet and 80 feet long and provides the bridge roadway 16 feet wide. It is designed to carry loaded log trucks weighing up to 250,000 pounds.
It has previously been suggested to provide portable bridges in the form of two separate longitudinal sections as shown in U.S. Pat. No. 854,329 of Charron. However, this bridge was designed for carrying automobiles and other small vehicles for military use in crossing ditches or trenches, and was only about 10 feet long or short enough to be carried on the side of the automobile during its travel. Such portable bridge employed two longitudinal bridge sections each formed of one piece of sheet metal which is not strong enough for transporting logging trucks and other heavy equipment. Among other things, the prior bridge does not employ a plurality of cross members extending across the top of longitudinal support members to provide each bridge section with a T-shape frame in the manner of the present invention. Furthermore, it does not employ pivoted rectangular diaphragm members for connecting the longitudinal bridge sections together, and whose opposite ends are fixedly secured to the bridge sections to prevent relative movement therebetween. Of course non-portable permanent bridges such as the railroad bridge shown in U.S. Pat. No. 498,994, have been made of heavy duty construction with steel I-beams which are bolted together on opposite sides of wooden cross members. These permanent bridges have employed bridge frame sections of H-shaped cross sections, which are fixed together by diagonal braces riveted to the I-beams and are extremely heavy so they are not portable.